Wide mouth plastic culture bottles or plastic bags are employed as containers for culturing edible mushrooms such as enoki mushrooms, beech mushrooms (bunashimeji), shiitake mushrooms, and the like.
When culture bottles are employed, these mushrooms can be cultured in the following way. First, the culture bottles are filled with culture medium, a cap having a filter is mounted on each culture bottle, and the bottles are then subjected to high-temperature sterilization. After the sterilization process, the culture bottles are cooled, the caps are removed after cooling and the culture medium is inoculated with inoculum, and the caps are again mounted on the bottles and the inoculum is cultured for a predetermined period of time. The caps are removed at the end of the culturing period, fruiting bodies are allowed to grow from the culture medium, and the mushrooms are harvested at the point in which they have attained a predetermined size.
A ventilation filter is placed in the cap mounted on the culture bottle or in the culture bag. The ventilation filter functions to prevent other fungi from contaminating the culture medium inside the culture container, and to exchange the carbon dioxide gas (CO2) generated from the mushrooms during the cultivation period with atmospheric air. The gas exchange characteristics of the ventilation filter is a big problem, particularly with respect to enoki mushrooms and the like, because they have a low tolerance to carbon dioxide gas and the ventilatory frequency of the carbon dioxide gas will have a conspicuous impact on culture quality.
When considered from this viewpoint, non-woven fabrics having comparatively good ventilation characteristics and low pressure drop are conventionally used as the ventilation filter medium.
However, ventilation filter media formed from a non-woven fabric or the like has an 80% collection efficiency with respect to 0.1 micrometer particles, and because the pore size thereof is large, cannot completely prevent fungal contamination even if the filter is mounted after the culture medium is sterilized, and in particular cannot completely prevent fungus such as Trichoderma from being propagated.
In addition, when other fungi have propagated inside the culture container, the other fungi propagated inside the culture container will pass through the ventilation filter media and leak out into the outside air and contaminate other nearby containers, mites propagated inside culture containers contaminated with other fungi will enter other culture containers, and other fungi, mites, and the like in the other culture containers will continue to spread.